Absorption refrigeration system having plural evaporators operable at different temperatures



APrl] 21, 1953 H. M. ULLSTRAND 2,635,437

ABSORPTION REFRIGERATION SYSTEM HAVING PLURAL EVAPORATORS OPERABLE ATDIFFERENT TEMPERATURES Filed Dec. 5, 1947 3 Sheets-Sheet l INV EN TOR.

Mar/745429 Aprll 21, 1953 ULLSTRAND 2,635,437

ABSORPTION REFRIGERATION SYSTEM HAVING PLURAL EVAPORATORS OPERABLE ATDIFFERENT TEMPERATURES Filed Dec. 5, 1947 3 Sheets-Sheet 2 IN V EN TOR.

HM WM Z%WM- arm/W5) pr 1953 H M. ULLSTRANO 2,635,437

ABSORPTION REFRIGERATION SYSTEM HAVING PLURAL EVAPORATORS OPERABLE ATDIFFERENT TEMPERATURES Filed Dec. 5, 1947 5 Sheets-Sheet 5 l A i I IiII/IIIIIIIII/IIIIIIIIIIIIIIIIIIIIII/11/11/16,

MMKM

Patented Apr. 21, 1953 ABSORPTION REFRIGERATION SYSTEM HAVING PLURALEVAPORATORS OPER- ABLE AT DIFFERENT TEMPERATURES Hugo Malcolm Ullstrand,Stockholm, Sweden, as-

signor to Aktiebolaget Elektrolux, Stockholm, Sweden, a corporation ofSweden Application December 5, 1947, Serial $10,789,893 In SwedenDecember 6, 1946 6 Claims. (01'. 62-99) My invention relates torefrigeration, and more particularly concerns cooling of subdividedcompartments of a refrigerator with the aid of a refrigeration systememploying evaporation of refrigerant fluid in the presence of an inertgas or auxiliary agent.

It is an object of my invention to provide improvements for cooling suchsubdivided compartments by a plurality of evaporators operable atdifferent temperatures, particularly to cool compartments subdivided bya horizontal partition whereby powerful low temperature cooling iseffected by one of the evaporators for freezing water and other matterto be frozen.

The above and other objects and advantages of the invention will be morefully understood from the following description taken in conjunctionwith the accompanying drawings forming a part of this specification, andof which:

Fig. 1 illustrates more or less diagrammatically an absorptionrefrigeration system of the inert gas type to which the invention isapplied;

Fig. 2 is a front elevation of a plurality of evaporators or coolingelements and connections thereto diagrammatically illustrating onepractical form of the evaporator structure shown diagrammatically inFig. 1;

Fig. 3 is a top plan view of the evaporators or cooling elements and theconnections thereto as shown in Fig. 2; and

Figs. 4 to 6 inclusive are fragmentary sectional views, looking towardthe rear of a storage space of a refrigerator, more or lessdiagrammatically illustrating different ways of embodying or associatingat least one of the evaporators in Figs. 2 and 3 in or with a horizontalpartition which serves to subdivide the storage space into a pluralityof compartments one above the other.

In recent years there has been a definite trend toward a householdrefrigerator of the kind in which the storage space is subdivided into aplurality of compartments one above the other which are arranged to becooled by a plurality of evaporators operable at different temperatures.The several subdivided compartments usually extend between the lateralside walls of the storage space, and one such subdivided compartment isadapted to be maintained at a low temperature for freezing water andother matter as well as for storing frozen food packages. In order toprovide a maximum amount of usable storage space in the subdividedcompartments the evaporators are more or less of horizontal shape and ofminimum height and at least one of the evaporators may be associatedwith the being referred'to as a window opening.

partition dividing the storage space into several compartments. 1 n,In'absorption refrigeration systems of the inert gas type havingevaporators adapted to operate at different temperatures, suchevaporators are generally formed by piping which are shaped as coils andconnected by conduits to other parts of the system for circulation ofinert gas as well as to supply liquid refrigerant to the evaporators.When such an absorption refrigeration system of the inert gas type isemployed in the cabinet of a household refrigerator, the evaporators andconnections thereto are usually inserted into the storage space throughan opening in a wall of the cabinet adapted to be closed by a closuremember, such wall opening often It is desirable to keep the windowopening as small as possible for practical reasons as well as to keep ata minimum the likelihood of heat leakage into the thermally insulatedinterior of the cabinet.

When an absorption refrigeration system of the inert gas type and havinga plurality of evaporators is employed in a household refrigerator ofthe kind referred to above, it will now be understood that it isdesirable to provide evaporator coils adapted to operate at differenttemperatures which are horizontally disposed and relatively close to oneanother to avoid an unduly large window opening. In such case it isdesirable to provide an arrangement in which the fluid connections tothe evaporators are as simple as possible. In accordance with myinvention, this is accomplished by providing low and higher temperatureevaporators through which inert gas or auxiliary agent circulates in thesame direction or in parallel flow with liquid refrigerant. In addition,provision is made for precooling liquid refrigerant which flows from thecondenser to the low temperature evaporator.

An absorption refrigeration system of the inert gas type to which theinvention is applicable is more or less diagrammatically shown inFig. 1. In order to simplify Fig. 1, the evaporator structure l2 hasbeen illustrated in a more or less conventional manner apart from ahousehold refrigerator having subdivided compartments one above theother. The manner in which evaporator structure l2 may be constructed inaccordance with the invention is illustrated in other figures of thedrawings and will be described hereinafter.

The absorption refrigeration system shown in Fig. 1 is of a uniformpressure type in which an inert gas or auxiliary pressure equalizingfluid is employed. In a system of this type a refrigerant fluid, such asliquid ammonia, for example, is introduced through a conduit 4-] intothe evaporator structure I2. The refrigerant fluid evaporates anddiffuses in the evaporator structure l2 into an inert gas, such ashydrogen, for example, to produce refrigeration and abstract heat fromthe surroundings.

The resulting gas mixture of refrigerant and inert gas flows from thecooling structure through an outer passage 14 of a gas ,heat .exchangerl5 and vertical conduit 116 into an absorber comprising a vessel l1 anda looped coil I 8. In the absorber vessel VI! and coil l8 refrigerantvapor is absorbed by a suitable absorbent, such as water, for example,which is introduced into coil [8 through a conduit .19. The hydrogen orinert .gas, which is practically insoluble and weak in refrigerant,returns to the cooling structure l2 through inner passage .20 of the gasheat exchanger 15 and a conduit 2|.

The circulation of gas in the :gas circuit ust described is due to thedifference in specific weight of the columns of gas rich and weak,respectively, in refrigerant vapor. Since the column of gasrich inrefrigerant vapor andflowing from evaporator structure l2 to theabsorber coil 18 is heavier than the gas weak'in refrigerant and flowingfrom' the absorber coil 18 to the-evaporator structure 12, a force isproduced or developed within the system for causing circulation of inertgas .in the manner described.

Form the vessel l1 enriched absorption liquid flows through a conduit-22 and an inner passage 23 of a liquid heat exchanger into the lowerend of a vapor lift tube 24 of a generator or vapor expulsion unit 25.The generator unit 25 comprises a heating flue 26 having the vapor lifttube 24 and a boiler pipe 21 in thermal exchange relation therewith, asby welding, for example. By heating generator unit 25,'as by a gasburner 28, for example, liquid from the inner passage 23 of the liquidheat exchanger is raised by vapor lift action through tube 24 into theupper part of the boiler pipe 21. The liberated refrigerant vaporentering boiler pipe 21 from the tube 24, and also vapor expelled fromsolution .in the boiler pipe, flows upwardly into an air cooledcondenser 29 provided with a pluralityof heat dissipating members orfins 30. Refrigerant vapor is liquefied in the condenser 29 and returnsto the evaporator structure l2 through the conduit H to complete therefrigerating cycle.

The weakened absorption liquid, from which refrigerant vapor has beenexpelled, is conducted from boiler pipe 21 through a conduit 3!, outerpassage 32 of the liquid heat exchanger and conduit 19 into the upperpart of the absorber coil [8. The lower end of the condenser 29 isconnected by conduit 33 to the gas circuit, as to the upper part ofabsorber coil l8, forexample, so that any non-condensable gas which maypass into the condenser can flow to the gas circuit and not be trappedin the condenser.

It will be understood that the cooling stucture l2 in Fig. 1 isdiagrammatically shown in the form of a coi1 and comprises a lowtemperature evaporator l2a and a higher temperature evaporator [2bhaving heat transfer members or fins 34 to provide a relativelyextensive .heat transfer surface. In Figs. 2 and v3 I have shown apractical form of the evaporator structure 12 in Fig. 1

which is suitable for abstracting heat from a plurality of subdividedcompartments disposed one above another in a storage space of ahousehold refrigerator. In order to simplify Figs. 2 and 3 and bring.out .more clearly the connections of the evaporatorstructure to otherparts of the refrigeration system, the manner in which the storage spaceis horizontally partitioned has not been shown, such partitioning beingillustrated in Figs. 4 to 6 which will be described presently.

In Figs. 2 and 3, in which parts corresponding to those shown in Fig. 1are designated by the same reference numerals, the evaporator structureI2 is horizontally disposed and includes two looped coils [2a and Nb atdifferent levels, the former serving as the low temperature evaporatorand the'latter as the higher temperature evaporator. The evaporatorstructure i2 is adapted to be positioned in a storage space 35 of arefrigerator cabinet which is indicated in dotted lines in Figs. 2 and3, the cabinet having thermally insulla'ted lateral :side walls '36, topwall 37 and rear wall 38. Each of the evaporator coils 12a and I2!) ispositioned in a single substantially horizontal plane and adapted toextend from one lateral side wall '36 to the opposite lateral side wallof the storage space. As best shown in Fig. 3, the gas heat exchanger I5is arranged exteriorly of the thermally insulated storage space 35, asin a vertical space usually provided at the rear of the cabinet, forexample, and desirably is embedded in insulation.

In the horizontal evaporator structure l2 of Figs. 2 and 3, inert gasweak in refrigerant flows from one passage of the gas heat exchanger l5through the conduit 2| which is connected at 39 to one end of the upperlooped coil 12a. Liquid refrigerant flows from the condenser through theconduit II which is also connected at 39 to the upper looped coil [2a.Inert gas and liquid refrigerant pass from the opposite end 40 of theupper looped coil 12a through a vertical conduit connection 4| to oneend of the lower looped coll l2b, the opposite end 42 of which isconnected by a conduit 43 to the outer passage of the gas heat exchangerin the manner diagrammatically shown in Fig. l.

The straight sections of the upper looped coil l2a are shown as beingparallel to the lateral side walls 36 and adapted to be at suchelevations that liquid refrigerant will flow by gravity from the point39 at one end to the point 40 at the opposite end of the coil. Thestraight sections of the lower looped coil I 2b are transverse to thestraight sections of the upper looped coil 12a and provided with heattransfer members or fins 34, the straight sections of the lower coilbeing at such elevations that liquid refrigerant will flow by gravityfrom the end section connected to the vertical conduit connection 4| tothe opposite end 42 through which inert gas rich in refrigerant passesfrom the evaporator structure I2.

In adapting the horizontal evaporator structure l2 of Figs. 2 and 3 in ahousehold refrigerator of the kind which is horizontally partitioned tosubdivide the storage space into a plurality of compartments one abovethe other, the low temperature evaporator l2a may be embodied in apartition which extends from one lateral side wall to the opposite sidewall of the storage space. Such an arrangement is shown in Fig. 4 inwhich the partition 44 comprises a casing 45 which subdivides thestorage space 35 into upper and lower compartments 46 and 41,respectively.

The casing 45 may be formed of suitable sheet metal and of such sizethat it extends substantially over the entire width of the space 35, andfrom the rear wall thereof toward the open front of the cabinet to aregion at which it is relatively close to the rear face of the cabinetdoor when the latter is in its closed position, so that circulation ofair between the upper and lower compartments 46 and 47 is substantiallyprevented. In addition, the upper compartment 46 may be provided with ahinged door (not shown) at the forward edge of the casing 45 arranged tobe resiliently biased to its closed position and readily opened bygrasping a part thereof. Suitable members 48 may be positioned at theinner sides of the lateral side walls36 to provide support for thecasing 45, if this should be desired. However, since refrigerationsystems of the type under consideration are formed of piping andconduits of ferrous metal which are connected together, as

by welding, for example, the upper coil or evaporator I211 will beself-supporting or self-sustaining in the storage space 35 and hence thecasing 45 does not actually require cabinet support, as by the members48, for example.

The upper coil or evaporator l2a is embodied in the casing 45 in suchmanner that it will primarily be effective to abstract heat from theupper compartment 46 which is defined by the partition M and thermallyinsulated walls of the storage space 35. In Fig. 4 this is accomplishedby'arranging the looped coil 12a in thermal exchange relation with theunderside of the upper or top horizontal wall of the casing 45. Suchthermal conductive connection of the casing 35 to the looped coil I266preferably extends continuously along the straight sections andconnecting bends of the coil. The casing 45 may be of such depth that agap is provided between the upper looped coil I211 and the bottomhorizontal wall of the casing, and the latter may be filled withsuitable insulating material 49 for thermally shielding the looped coiliZa from the lower compartment ll and looped coil |2b horizontallydisposed in the upper part thereof. In this way the lower looped coil orevaporator [2b will be primarily efiective to abstract heat from thelower compartment 41.

The partitioning of the storage space 35 may be effected in a variety ofways. Another manner of partitioning the storage space is illustrated inFig. 5 which differs from Fig. 4 in that no insulating material isprovided in the interior of the casing 45'. In Fig. 5 the straightsections and connecting bends of the upper looped coil in are in goodthermal contact along the entire length of the coil to the underside ofthe top horizontal wall of the casing d5, as by brazing, for example. Agap may or may-not be provided between the upper looped coil lza and thebottom horizontal wall 56 of the casing 55' which is formed of materialhaving poor thermal conducting properties, such as a synthetic resinoussubstance, for example. By providing such a bottom 50 for the casing45', the upper and lower compartments i8 and 4'! are thermally shieldedand segregated from one another whereby each of the evaporators !2a andlZb will be primarily effective to abstract heat from one of thesubdivided compartments.

Another manner of thermally segregating the upper and'lower compartments46 and Al is shown in Fig. 6 which differs from the arrangementspreviously described in that the upper looped coil I'Za is disposed inthe metal casing 45' to the bottom horizontal wall of which is fixed alayer of thermal insulation 5! in anysuitable manner. As shown, suchthermal insulation layer 5! may be arranged to rest on the side members48 for laterally supporting the upper evaporator IZa although this isnot necessary, as previously explained.

In accord with my invention liquid refrigerant flows downwardly in theupperloop coil or evaporator 52a. and also in the lower looped coil orevaporator l2b in the presence of and in parallel flow with inert gas.This will be evident when reference is made to Figs. 2 and 3 in whichliquid refrigerant conducted through conduit II and inert gas flowingthrough conduit 2! enter the upper looped coil I 2a at the point 39 andflow in the same direction through such coil to the point as at theopposite end thereof.

Unevaporated refrigerant is conducted from the upper looped coil l2athrough the vertical conduit connection 4| into one end of the lowerlooped coil 2b, and such refrigerant and inert gas continues to flow inthe same direction and in parallel fiow through the lower looped coill2b to the point 42 from which the mixture of inert gas and refrigerantvapor passes from the evaporator structure. Since the inert gas flowssuccessively through the evaporators In and l2b, the gas in the upperevaporaor I'Za contains a lesser amount of refrigerant vapor than thegas in the lower cooling element I222. The partial vapor pressure of therefrigerant is a gradient, whereby the temperature of liquid refrigerantis also a gradient, the evaporating temperature of liquid being lower inthe upper cooling element 12a which constitutes the freezing section ofthe evaporator structure.

The upper compartment 46 may, therefore, be referred to as a freezingspace adapted to receive ice trays, frozen food packages and othermatter to be frozen, the top horizontal wall of each of the casings inFigs. 1, 5, and 6 being substantially flat and serving as a supportingshelf for the upper freezing compartment. The lower evaporator !2b,which is the higher temperature section of the evaporator structure, iseffectively utilized to cool air in the lower compartment 41.

One of the major requirements in horizontally disposed evaporators ofthe type just described is to provide a low temperature evaporator whichwill be highly effective to produce low temperature cooling for thefreezing space. In horizontally disposed evaporator structure ithasgenerally been the practice heretofore toconnect the low temperatureevaporator coil or section to other parts of the system in such mannerthat inert gas flows therethrough in counterflow to liquid refrigerant.When the low temperature evaporator is connected in the system in suchmanner that inert gas and liquid refrigerant pass therethrough inparallel flow, it would be expected that the mean or average temperatureof the low temperature evaporator would be sufficiently disturbed byreason of the fact that inert gas weak in refrigerant and flowing fromthe gas heat exchanger to the low temperature evaporator passes into thepresence of liquid refrigerant without previous cooling. Even thoughinert gas weak in refrigerant flows from the gas heat exchanger into thelow temperature evaporator and no provision is made for abstracting heattherefrom prior to coming into the presence of liquid refrigerant, ithas been found that low temperature evaporators connected for parallelflow of liquid refrigerant and inert gas and embodied in or associatedwith a horizontal partition, as disclosed herein, are highlysatisfactory and capable of producing powerful low temperature cooling'for freezing purposes.

When liquid refrigerant entering the upper looped coil or lowtemperature evaporator l2a is precooled, evaporation of liquidrefrigerant will take place at a lower temperature at the gas and liquidinlet end of the upper looped coil. Such provision for abstracting heatfrom liquid refrigerant in its path of fiow from condenser 30 may beaccomplished by arranging the conduit II in thermal exchange relationwith the coil of the low temperature evaporator i2a, or in thermalexchange relation with the fins 34 of the higher temperature evaporatorl2b. For maximum precooling of liquid refrigerant, the conduit II may bearranged in thermal contact with both the fins 34 and the coil of thelow temperature evaporator I2a.

In Fig. 1 this is diagrammatically shown by the thermal contact of theconduit H with a fin 34, as indicated at 52, and the thermal contact ofthe conduit II with the coil of the low temperature evaporator structure1 2a, as indicated at 53. In the horizontally disposed evaporatorstructure in Figs. 2 and 3, one part of the conduit ll may be arrangedparallel to the straight coil section of the higher temperatureevaporator [2b which is adjacent to the rear wall of the cabinet andpass through openings in fins 34. A good thermal connection 52' may beprovided in any suitable manner between the conduit i l and each fin 34through which it extends. Also, another part of conduit I! may bearranged in thermal contact with the upper looped coil I'Za, asindicated at 53'. By first passing in thermal transfer relation with thefins 34 of the higher temperature evaporator I21) and then passing inthermal transfer relation'with the coil of the low temperatureevaporator lZa, liquid refrigerant is effectively precooled beforepassing into the presence of inert gas at the point 39 of the lowtemperature evaporator [211.

Even when no precooling liquid refrigerant is effected in the mannerjust described, it should be understood that horizontally disposedevaporator structure like that described above and embodied in orassociated with a horizontal partition has been found to be highlysatisfactory for low temperature cooling purposes. When the lowtemperature evaporator is connected for parallel fiow of inert gas andliquid refrigerant therethrough, an important advantage is gained inthat the connections for circulating :fiuids through the low and highertemperature evaporators are simplified to a great extent.

Modifications of the embodiments of my invention which I havedescribedwill occur to those skilled in the art, so that I desire myinvention not to be limited to the particular arrangements set forth.Therefore, I intend in the claims to cover all those modifications whichdo not depart from the spirit and scope of my invention.

What is claimed is:

1. In the art of refrigeration with the aid of an absorptionrefrigeration system having first and second evaporators. in whichliquid refrigerant evaporates in the presence of an inert gas, theimprovement which comprises flowing liquid refrigerant solely by forceof gravity through said first and second evaporators, fiowing inert gasin parallel with liquid refrigerant in said first evaporator in acircuitous path of fiow extending substantially horizontally over amajor portion of a first definite cross-sectional area at one'level,introducing inert gas and liquid refrigerant to said second evaporatoronly from said first evaporator, flowing inert gas and liquidrefrigerant in said second evaporator in a circuitous path of fiowextending substantially horizontally over a major portion of practicallythe same definite cross-sectional area at a different level in verticalalignment with said first area, effecting said flow of inert gas throughsaid first and second evaporators by force resulting solely from thedifference in specific weight of columns of gas rich and weak,respectively, in refrigerant vapor, and utilizing said evaporators tocool different places segregated from one another.

.2. In the art of refrigeration with the aid of an absorptionrefrigeration system having first and second evaporators in which liquidrefrigerant evaporates in the presence of an inert gas, the improvementwhich comprises flowing liquid refrigerant solely by force of gravitythrough said first and second evaporators, fiowing inert gas in parallelfiow with liquid refrigerant in said first evaporator in a circuitouspath of flow extending substantially horizontally over a major portionof a first definite cross-sectional area at one level, introducing inertgas and liquid refrigerant to said second evaporator only from saidfirst evaporator, fiowing inert gas in parallel fiow with liquidrefrigerant in said second evaporator in a circuitous path of fiowextending substantially horizontally over a major portion of practicallythe same definite cross-sectional area at another lower level invertical alignment with said first area, effecting said flow of inertgas through said first and second evaporators by force resulting solelyfrom the difference in specific weight of columns of gas rich and weak,respectively, in refrigerant vapor, utilizing said first evaporatorprimarily to cool a first place, and utilizing said second evaporatorprimarily to cool a second place which extends beneath said first placeand is segregated therefrom.

3. An absorption refrigeration system of the inert gas type including alow temperature evaporator connected for fiow of inert gas in parallelwith liquid refrigerant, ahigher temperature evaporator provided with arelatively extensive heat transfer surface, and a conduit for supplyingliquid refrigerant to said low temperature evaporator having one partthereof in heat transfer relation with said heat transfer surface andanother part in heat transfer relation with said low temperatureevaporator for precooling liquid refrigerant supplied to said lowtemperature evaporator.

4. An absorption refrigeration system as set forth in claim 3 in whichsaid liquid refrigerant conduit is in heat transfer relation with spacedapart regions of said low temperature evaporator.

5. A refrigerator comprising a cabinet having an inner liner defining astorage space and thermally insulated walls disposed about such liner,an absorption refrigeration system containing inert gas in the presenceof which refrigerant fluid evaporates, said system including a condenseroutside the storage space at a level below the top of the cabinet andlow and higher temperature evaporators comprising substantiallyhorizontally disposed looped coils positioned relatively near to oneanother at different levels in said space in the upper part thereof,means for conducting refrigerant fiuid from said condenser to said lowtemperature evaporator and said higher temperature evaporator forgravity 'fiow therethrough, a partition including a horizontallydisposed member having the looped coil forming said low temperatureevaporator as a unitary part thereof to subdivide said space into anupper freezing compartment extending upwardly from the top surface ofsaid member and a larger lower food storage compartment extendingdownwardly from the bottom surface of said member to abstract heat fromsaid freezing compartment primarily by said low temperature evaporatorand abstract heat from said food storage compartment primarily by saidhigher temperature evaporator, said higher temperature evaporatorreceiving inert gas from said low temperature evaporator and the latterbeing connected in the system for parallel flow of inert gas with liquidrefrigerant, said horizontally disposed member serving as the bottom orfloor of said freezing compartment for supporting ice trays and frozenfood packages and the like, said higher temperature evaporator beingprovided with a relatively extensive heat transfer surface, and saidmeans for conducting liquid refrigerant from said condenser to said lowtemperature evaporator including a conduit having one part thereof inheat transfer relation with said heat transfer surface and another partin heat transfer relation with said low temperature evaporator forprecooling refrigerant fluid supplied to said

